<%@ page import="javax.security.auth.callback.Callback" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8"%>
<%
    String callback = request.getParameter("callback");
    if( callback == null || "".equals(callback) ){
        out.print("{\"abc\":123}");
    }
    else {
        out.print(callback + "({\"abc\":123})");
    }
%>